AU2011238158B2 - Coaxial conductor structure - Google Patents

Abstract

The invention relates to a coaxial conductor structure for interference-free transmission of a TEM mode of a HF signal wave within at least one band of n frequency bands forming in the context of a dispersion relation, with n as a positive natural number, with a) an internal conductor comprising a round cross-section having an internal conductor diameter D

Description

Coaxial Conductor Structure Technical Area The invention relates to a coaxial conductor structure for interference-free transmission of a TEM fundamental mode of an HF signal wave. Prior Art The transmission quality of coaxial conductors for the TEM fundamental mode of HF signal waves diminishes with rising signal frequencies, especially since, at higher frequencies, mode conversion processes along the coaxial line lead to undesired, propagable modes of a higher order, e.g., TE 11 , TE 21 modes, etc., which become superimposed with the TEM fundamental mode. For example, an article by Douglas E. Mode entitled "Spurious Modes in Coaxial Transmission Line Filters", Proceedings of the I.R.E., Vol. 38, 1950, pp.176-180, DOI 10.11090/JRPROC.1950.230399, examines the lower frequency limit for an interference-generating, lowest TE mode along a coaxial line, along which so-called shunt inductors are secured in the form of internal and external conductors of the coaxial line. In order to analytically determine the lower frequency limit, simplified assumptions are made, or a modified rectangular waveguide representing the coaxial line is taken as the basis. No dispersion relations are calculated for the TEM and TE 11 mode. In particular with respect to future expansions or modifications of existing transmission ranges for HF signals, stipulated in the frequency utilization plan for the Federal Republic of Germany, to higher frequencies, measures must be found to enable as interference-free, high-frequency a signal transmission of the TEM fundamental 1 mode of HF signals as possible via coaxial lines with the largest possible diameter. The set objective is resolved as indicated in claims 1 and 4. Advantageous configurations and further developments of the coaxial structures according to the solution are specified in the subclaims, and also described in the further specification, drawing reference to the exemplary embodiments. The coaxial conductor structure according to the solution proceeds from the knowledge that the transmission behavior of coaxial lines changes significantly for HF signal waves if electrically conductive connecting structures are introduced between the external and internal conductor at respective periodically equidistant intervals along the coaxial line. As revealed by an examination of the propagation behavior of the TEM fundamental mode along a conventional coaxial line, i.e., the external and internal conductor are electrically insulated by the interspersed dielectric, within the framework of a dispersion diagram, a linear correlation exists between the frequency respectively the circuit frequency o and the propagation constant P of the HF signal wave with the form es (- , i.e., co=c$. This linear correlation is manifested as a so-called light speed line in a dispersion diagram o($). Starting at a lower frequency limit, the so-called cut-off frequency (fco) for the TE 11 mode, rising frequencies are accompanied by the formation along the conventional coaxial line of undesired propagation modes of a higher order,

TE

11 , TE 21 , TE 31 , TE 4 1 , TMo 1 , TM 11 , etc., so that the TEM base mode is always superimposed by modes with a higher order of excitation at frequencies exceeding fco. By contrast, providing electrically conductive structures between the external and internal conductor of the coaxial line in the manner indicated above leads to the formation 2 of frequency bands in which the TEM fundamental mode is able to propagate, along with band gaps lying between the frequency bands, in which the TEM fundamental mode is evanescent, i.e., unable to propagate. Even though this result would at first glance appear disadvantageous, especially since the frequency-specific transmission range for the TEM fundamental mode is curtailed by comparison to a conventional coaxial conductor, this disadvantage can be used in accordance with the solution. In addition, it has been found that adding the electrically conductive connecting structures between the external and internal conductor of the coaxial line causes a frequency windowing of the TEM fundamental mode into respectively specific, propagable frequency bands as described above, even at the excitation modes of a higher order, i.e., even the higher excitation modes, TE 11 , TE 21 , etc. are accompanied by the formation of frequency ranges in which the modes are propagable, and other frequency ranges in which they are evanescent. The idea underlying the invention is based on the consideration that, by selecting the right structural design parameters for setting up a coaxial line with electrically conductive connecting structures between the external and internal conductor, the frequency-dependent positions of the frequency bands denoted above can be specifically and controllably influenced in such a way that at least one frequency band in which the TEM fundamental mode is propagable can be made to cover or overlap a frequency band or range in which all excitation modes of a higher order are evanescent. In order to further establish the terminology, it is assumed that a number "n" of specific frequency bands in which the TEM fundamental mode is propagable forms in the coaxial conductor structure according to the invention to be described. The counting parameter "n" here starts at 3 one, and represents a natural, positive number. In like manner, "m" specific frequency bands form, in which the

TE

11 mode is propagable, wherein "m" also represents a positive, natural number as the counting parameter. While we will refrain from any further discussion relating to the appearance of higher order excitation modes, especially since the latter arise at frequencies whose technical applicability is regarded as less relevant, at least at present, these excitation modes can also be taken into account in an equivalent application of the inventive idea. A coaxial conductor structure designed according to the solution for the interference-free transmission of a mono mode TEM fundamental mode of an HF signal wave in at least one band of n frequency bands that form within the framework of a dispersion relation exhibits the following components: a) An internal conductor with a preferably circular cross section and an internal conductor diameter Di, although cross sectional forms that approximate a circular shape are also conceivable, e.g., with an n gonal circumferential contour, b) An external conductor that radially envelops the internal conductor with an external conductor inner diameter Da, preferably in a radially equidistant manner, although cross sectional forms that approximate a circular shape are also conceivable, e.g., with an n-gonal circumferential contour, and c) An axially extending, common conductor section of the internal and external conductor, along which, in equidistant intervals p, s rod-shaped structures with a rod diameter Ds that electrically connect the internal conductor with the external conductor are provided each. While rods with a circular cross 4 section are preferably suitable, the rod cross sections can also be n-gonal or the like. In order to allow the TEM fundamental mode to propagate along the coaxial conductor structure unimpeded by higher excitation modes, which arise at least in the form of a TE 11 mode within m frequency bands, the above parameters Di, Da, Ds, p, s must be selected in such a way that the following two conditions are satisfied: i) A lower cut-off frequency fu(TEM) of the TEM mode propagating within an n 2 -nd band is equal to an upper cut-off frequency fo(TE 11 ) of the forming TE 11 mode in the m-th band, and ii) An upper cut-off frequency fo(TEM) of the TEM mode propagating within an n 2 -nd band is equal to a lower cut-off frequency fu(TE 11 ) of the TE 11 mode forming within the (m+l)-th band. In terms of the solution, the above required mathematical relations must be regarded as somewhat softened, i.e., a technically acceptable mono-mode propagation of the TEM mode can also be used if the following applies: i) If,(TEM, n) - f,(TE1 1, m)< (f, (TEM, n) - f,(TEM, n)) 3 as well as ii) If,(TEM,n)-f,(TE11,m+1)|<I(f(TEM,n)-f.(TEM,n)) 3 As has been demonstrated, a technical utilization of the TEM mode without any notable loss in quality is possible in an area where the propagable TEM mode slightly overlaps the

TE

11 mode. This tolerance range Af measures at most 1/3 of the n-th TEM bandwidth. 5 It has further been shown that the measures according to the solution for creating a frequency window that is able to propagate without interference for the EM mode along a coaxial conductor structure can also be successfully applied for a coaxial conductor structure in which the internal conductor and/or external conductor cross section of the coaxial line deviates from the circular shape, but exhibits the same wave resistance as the round coaxial line. For example, the external and internal conductor cross section can here be n-gonal. However, the other considerations relate to respectively circular cross sectional shapes. As the further statements will demonstrate, suitably selecting the structural design parameters Di, Da, Ds, p, s makes it possible to establish coaxial conductor structures that enable a completely interference-free propagation of the TEM fundamental mode in frequency ranges exceeding the cut-off frequency fco of the TE 11 mode without any higher order excitation modes, and do so at frequencies so high that higher order excitation modes would be unavoidable in conventional coaxial conductors. In like manner, giving the coaxial conductor structure according to the solution a suitable structural design makes it possible to shift the cut-off frequency fco to higher frequency values, and in so doing expand the first frequency band in which the TEM fundamental mode is mono modally propagable toward higher frequencies. Such a coaxial conductor structure according to the solution is characterized by the structural design parameters Di, Da, Ds, p, s elucidated above, wherein these parameters must be selected in such a way that an upper cut-off frequency fo(TEM) of the TEM mode propagating within the first, i.e., n=1, band is less than or equal to the lower cut-off frequency fu(TE 1 1 ) of the forming TE 11 6 mode in the first band, i.e., m=l, wherein the following applies: fo(TEM)= and fu(TE 11 )= a f +f, , so that 2p 3+a C 6a 2 - :5 ffC. 2p 3+a The following applies here: c c 2 sZ p"' 1 P f- fc 2 and a SI" undZ - - f " . 2x7p D + D, 2 cLod 2r e D, We will assume for the above correlations that c represents light speed in the dielectric, normally air. Let it be noted for this coaxial conductor structure according to the solution that the lower frequency limit of the TE 11 in the first band, and hence the mono-mode TEM operation, 6a 2 increases to f,(TEu)= f +f 0 2 by comparison to fu(TE 11 )=fe, of a 3+a conventional coaxial line. In addition to the design criteria for coaxial conductor structures outlined above, which quite essentially provide for using the electrically conductive structures that connect the external and internal conductors, and at least in certain frequency bands enable interference-free transmission properties exclusively for the TEM fundamental mode, precisely the electrically conductive structures help to specifically cool the internal conductor, which is subjected to considerable warming in particular during the transmission of powerful HF signals. Since the electrically conductive connecting structures preferably consist of rod-shaped structures made out of a metal material, preferably the same material the internal and/or external conductor are consisting of, they exhibit a high 7 thermal conductivity. As a consequence, electrically conductive materials are suitable for these structures, which have an especially high thermal conductivity. The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application. Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps or components, or group thereof. Brief Description of the Invention The invention provides a coaxial conductor structure for interference-free transmission of a single propagable TEM mode of an HF signal wave within at least one band of n frequency bands forming within the framework of a dispersion relation, with n as a positive natural number, with a) an internal conductor exhibiting a circular cross section, with an internal conductor diameter Di, b) an external conductor that envelops the internal conductor in a radially equidistant manner, with an external conductor inner diameter Da, c) an axially extending, common conductor section of internal and external conductor, along which, in equidistant intervals p, s rod-shaped structures 8 with a rod diameter Ds that electrically connect the internal conductor with the external conductor are provided , wherein, in order to allow the single TEM mode to propagate along the coaxial conductor structure unimpeded by higher excitation modes, which arise at least in the form of a TE 11 mode within m frequency bands, the parameters Di, Da, Ds, p, s can be selected in such a way that i) A lower frequency limit fu(TEM) of the single TEM mode propagating within an n 2 nd band is equal to an upper offset frequency fo(TE 11 ) of the forming TE 11 mode in the m-th band ± of a tolerance range Af, and ii) An upper cut-off frequency fO(TEM) of the single TEM mode propagating within an n 2 -nd band is equal to a lower cut-off frequency fu(TEii) of the forming TE 11 mode in the (m+l)-th band of a tolerance range Af. The invention further provides The coaxial conductor structure for the interference-free transmission of a single TEM mode of an HF signal wave within at least one band of n frequency bands forming within the framework of a dispersion relation, with n as a positive natural number, with a) an internal conductor exhibiting a circular cross section, with an internal conductor diameter Di, b) an external conductor that envelops the internal conductor in a radially equidistant manner, with an external conductor inner diameter Da, 8a c) an axially extending, common conductor section of internal and external conductor, along which, in equidistant intervals p, s rod-shaped structures with a rod diameter Ds that electrically connect the internal conductor with the external conductor are provided , wherein, in order to allow the single TEM mode to propagate along the coaxial conductor structure unimpeded by higher excitation modes, which arise at least in the form of a TE 11 mode within m frequency bands, with m as a positive, natural number, the parameters Di, Da, Ds, p, s can be selected in such a way that that an upper cut-off frequency fo(TEM) of the single TEM mode propagating within the first, i.e., n=1, band is less than or equal to the lower cut-off frequency fu(TE 11 ) of the forming TE 11 mode in the first band, i.e., m=l, wherein the following applies: =c adudf(E 1 6a f 0 (TEM) = - and und f.(TEn) = fa2+f2 so that the following 2p 3+a applies: C 6a 2 2p 3+a with c c 2 SZp.1.pD f= ,f=- and a= 7'" and Z 7 ,M 21p ;r D,, + D, 2cLro 21r E D Brief Description of the Figures The invention will be described by example below based on exemplary embodiments, making reference to the drawings, and without in any way limiting the general inventive idea. 8b Fig. 1 Depiction of a section of a coaxial conductor structure designed according to the solution, and Fig. 2 TEM dispersion diagram, Fig. 3 Diagrammatic depiction of the Bloch impedance for the TEM mode, as well as Fig. 4 Diagram with all dispersion relations up to a specific maximum frequency. Comparison of the equivalent circuit diagram with a full-wave EM simulation. Ways of Implementing the Invention, Commercial Applicability Fig. 1 presents a section of a coaxial conductor structure designed according to the invention. The section represents a kind of elementary cell for building up a coaxial line, which in the end is characterized by a periodic return of the illustrated section. The transparently depicted external conductor AL exhibits an external conductor inner diameter Da, and incorporates an internal conductor IL having a length p, a circular conductor cross section and an internal conductor diameter Di. Provided central to the longitudinal extension p of the internal conductor IL are s = 2 rod-shaped structures S, which establish an 8c electrically conductive contact or electrically conductive connection with the external conductor AL. The rod-shaped structures S are made out of an electrically and thermally readily conductive material, preferably metal, especially preferably out of the same material used to fabricate the internal or external conductor. The structures S can exhibit a circular or n-gonal cross section. Let it be assumed for the continued mathematical analysis that the structures exhibit diameter Ds. It is basically possible to provide a single, i.e., s=l, rod-shaped structure S per elementary cell. Further deliberations and corresponding computations demonstrate that especially favorable transmission properties for the coaxial line are achieved when s=2, 3 or 4. In the case of s=l or s=2, it makes sense to arrange the rod-shaped structures situated in respectively equidistant intervals p along the coaxial line relative to the circumferential direction of the internal and external conductor in such a way that the rod-shaped structures are each congruently located one behind the other in an axial projection to the axially extending, common conductor section, or each offset at an identical angular misalignment Ao oriented in the circumferential direction of the internal and external conductor IL, Al. For example, in the case of s=l or 2, it is advantageous to arrange two axially sequential rod shaped structures twisted by Aa = 900 around the coaxial conductor longitudinal axis, so as to minimize potential magnetic couplings between the rods. The elementary cell depicted on Fig. 1 for building up a coaxial line according to the solution will be used below to describe the electromagnetic design of such a line, so as to be able to tailor desired dispersion relations of the technically used TEM fundamental mode and interfering TEll mode. The goal is to design coaxial conductor structures with relatively large diameters Da, which have only a 9 single propagable mode, specifically the TEM fundamental mode, in a desired frequency range bounded by a lower fu and upper fo cut-off frequency. All other modes in this frequency range are to be evanescent. The advantage of the symmetrical elementary cell shown on Fig. 1 is that its input impedances at input E and output A are identical. The cell consists of two lines L1, L2 with impedance Z=ZF=- . -WIn "l, propagation constant y=J 2r e D, c and length l=p/2 and an interspersed shunt admittance Y=1/jmoL. The rods can be described by approximation using an inductance L as L = o, Ld "D - n "D , , wherein s is the number of s 2 4;r D, radial rods. The individual sections of the elementary cell, L1, L, L2, can be described by ABCD matrices, which can be simply cascaded through matrix multiplication. The ABCD matrix for line Li, L2 is given by ABCD77 cosh(#) Z sinh(g) ABCD z = 1 I and the shunt inductance L by ABCDL= I jo)L ' (2) For the entire elementary cell, this yields A BCD,,, = A BCD, A BCD, A BCDJ (3) 10 The Bloch analysis can now be performed, during which periodic boundary conditions are used, i.e., voltage + current at the output is equal to voltage + current at the input multiplied by a phase factor exp(jp). This yields = ABCD,,, U2 = )2 U 2 2(4) and reveals an eigenvalue problem with two eigenvalues e". It here turns out that (, =-( 2 , applies, i.e., a respective forward and reflected wave is involved. The following determinants must disappear to calculate the eigenvalue: A-e* B =0 C D-e el' (5) A lengthier computation yields Cos-+ sin-CcosP c 2wL C (6) It here makes sense to normalize the frequency to x= = 2 f , yielding C C a. cosx+-simx=COSI9 x (7) Zp wherein a=- represents a dimensionless parameter for the 2cL so-called perturbation by L. This equation (7) can be solved for p . Finally, plotting x via (p(x)=arccos cosx+ - sinx x results in the TEM dispersion diagram depicted on Fig. 2, shown here for different values of a. As clearly evident, the periodic shunt inductance generates bands B and band gaps BL. A TEM wave is propagable in the bands B, while the wave is evanescent and attenuated at frequencies within a band gap. Obtained for a=O (i.e., L becomes infinite, transverse rods disappear, dashed curve) is the typical light speed line c f= (p of the interference-free coaxial line, which is 2np folded into the first Brillouin zone along a zigzag pattern. The other extreme case is at a=oo, L=0: Obtained here are uncoupled line resonators having length p and resonance frequencies x=nn, i.e., X/2resonators. The bands here shrink together into dot frequencies. Subjecting the left side of the equation (7) to series expansion at points x=nn up to the 2 nd order and having it be equal to (-l)" makes it possible to calculate the cut off frequencies (fu, fo) of the individual bands by approximation for small perturbations a<<3n, yielding as follows for the first band with the lowest frequency: x 6a 3+a (8) And for the n-th band with n>l: x,,=nxr 2a/(n--1)/if 2a__ x,, ((n- -1)/ 2 ~(n-1)7f+ 2a 1+2a/(n -1)2 /I (n -1)r (9) 12 By contrast, the following is obtained at very large perturbations a>>3n for the n-th band (n>=l): x,, =nxz n2a 8 4n 2 "'"n2,r2+2a pa aa2 (10) As a result, TEM dispersion has been completely characterized, and can be tailored as a function of the geometry. A band will typically be used for transmission in such a way that the actually usable frequency range distinctly exceeds the one required. This makes it possible to compensate for production tolerances, minimize high insertion losses owing to the disappearing group velocity (slope=O)at the band limits, and minimize high reflections owing to the increasing deviation of the frequency-dependent Block impedance from the target impedance at the band limits. The so-called Bloch impedance ZB is the effective impedance of the periodic line; it is the input impedance of an infinitely long periodic structure. In order to connect the periodic structure to a conventional coaxial line with impedance Zw in as reflection-free a manner as possible, ZB should come as close as possible to Zw. The Bloch impedance can be calculated from the voltage and current of an elementary cell at periodic boundary conditions, i.e., from the two components of the eigenvector of the eigenvalue problem (4): sin -+ 1kM I-cos I U U B B C 2 WL,, \. C Z '(0))=-'-=2=- =- = =ZT 11 /2 A-e" P 2_ 2 1- cos-E(9+ Z' sinpo c 2wL7,*M c 13 The diagram illustrated on Fig. 3 depicts the strong frequency dependence of the Block impedance ZB, which can deviate to an extreme from the impedance of the interference-free coaxial line ZTEM. This example used a=7.8, p=72mm and ZTEM = 2 8 . ZB is purely imaginary in the band gaps BL, as it should be for a reactive load that absorbs no active power. In contrast, ZB is real in the transmission bands B and moves ever closer to the value for the interference-free line ZTEM in the higher bands, where perturbation arising from the inductances has a weaker effect. Clearly evident as well is how the Bloch impedance becomes negative in the even numbered bands, which has to do with the negative group velocity (i.e., slope do/dp < 0), so that the current changes its sign. A periodic structure will preferably be conceived in such a way that the reflection r= ZB-Zw remains less in terms ZB +Z, of amount than a given rmax in the transmission range B, for example Ir|<ra.=0,1. This represents a secondary condition for determining or optimizing the geometric parameters. The TE 11 mode can be modeled similarly to the TEM fundamental mode described above, especially since the structural design of the elementary cell and the equivalent circuit diagram associated therewith is the same as in the case of the TEM fundamental mode, only the propagation constant and impedance become highly dependent on frequency with respect to the waveguides: InD Dp Z(f)= - , (12) 4f If2 14 7AD _ 21f If Fi 1, /7 C with the approximated TE 11 cut-off frequency C 2 ir D, + D, If the same calculation as in the TEM case is performed similarly to (6), the following equation is obtained for the TE 11 mode: W2 2 ZJI 1-W 0 If 2 If cos- 1-f2/f2+2sin- -fe 2 =cos c 2aLs C ( 13) Since the same root appears in the impedance and the propagation constant, a transformation to a normalized frequency x can be performed as in the TEM case, and the same equation is in fact obtained once again co0s x + sin xT =cos (14) but now with the normalized frequency C or -1 2 Z7;,M p x 1 c +fe, aT c 27rP and with the perturbation cL If four, i.e., s=4, radial rods are used to prevent mode conversion TEM<->TE11, as in a preferred application, = Lro d /4 and LTE = Lrod ,/2 since the TEll wave only "sees" two rods arranged parallel to the E-field. However, the perturbation parameter becomes identical in both cases as a 2 ZILmP result: cL'-d , which in turn means that the 15 normalized cut-off frequencies (xu, xo) of the TEM and TEll bands are the same! As a result, the bottom line is that the dispersions of TEM and TEll modes in periodic structures with four connecting structures are very tightly interlinked. The only parameter that makes it possible to individually influence both modes is the cut-off frequency fco of the TEll mode in the coaxial line, which upwardly shifts the TEll bands. The following tables summarize the (non-normalized) cut-off frequencies of the TEM and TE 11 bands of 4-rod geometries: Small perturbation a<<3n Mode Band Lower cut -off frequency Upper cut-off frequency TEM 1 a ffo 3+a n 2a/(n-1)/r n f, 1+2a /(n -1)2 17r2

TE

11 1 6a f2 +f(fO) 2 +f2 3+a m 2a(n-)/n 2 2 + n f 2f m n - ) + - 2 l n I l r f 2 + f 2 ( rf ((n 1+2a/(n-_1)2 / 2 co Large perturbation a>>3n Mode Band Lower cut-off frequency Upper cut-off frequency TEM n na 8 4n22 nxf n27r2 +2a a a2 A

TE

1 1 m M ,(nucfn 2 coY c c 2 wherein f C - , - 2 and the peturbation is 2xzp 7rD + D, a= 2Z 1 m p cLr 16 The following applies with respect to ZTEM: Z7;M =_i 2;r D, The dispersion relation depicted on Fig. 4 shows an excellent correlation between the equivalent circuit diagram description and a full-wave simulation for a coaxial conductor structure having a respective four connecting rods per elementary cell and the additional dimensions Da=36mm, Di=22.8mm, p=72mm, Ds~1.5mm, with a pure rectangular rod measuring lx2mm; Lrod=1.

6 8nH was here extracted from a numerical model by means of CST (computer simulation technology). The solid curves correspond to the TEM dispersion bands n=1,2,3,4, and the dashed curves show the TE 11 dispersion bands m=1,2,3,4, wherein both a CST simulation and ESB calculations (ESB: equivalent circuit diagram) were performed for both curves. Especially the four smallest bands are modeled to nearly match the stroke width! In the dispersion relation presented on Fig. 4, it makes sense to use the 3 rd TEM band (n=3) for transmission, more precisely the distinctly smaller frequency range FR of 5.4 to 5.9 GHz. Since as large a mono-mode frequency range as possible is most often desired, the used TEM band should be as broad as possible, as should the TEll band gap as well. However, since the TEM mode cannot be influenced independently of the TEll mode, as was demonstrated above, the compromise will involve perturbation a in the transition area a~3n, making the band width and band gap about the same size. In such a conductor geometry, the perturbation at a=7.8 lies precisely in the transition area, where both approximation formulas become imprecise for the cut-off frequencies, as summarized in the above table. Despite this fact, the cut off frequencies of the two lowest bands can preferably be calculated using the formula for the large perturbation. At the higher bands with n>2, the formulas for the small 17 perturbation are more accurate. Of course, a numerical procedure, e.g., Newton's method, yields precise results. 18 Reference List CST Computer Simulation Technology ESB Equivalent circuit diagram E Input A Output Ll, L2 Conductor inductance L Shunt admittance S Structure, connecting structure AL External conductor IL Internal conductor Da External conductor inner diameter Di Internal conductor (outer) diameter Ds Rod diameter p Elementary cell length BL Band gap B Band 19

Claims (13)

1. A coaxial conductor structure for interference-free transmission of a single propagable TEM mode of an HF 5 signal wave within at least one band of n frequency bands forming within the framework of a dispersion relation, with n as a positive natural number, with a) an internal conductor exhibiting a circular cross 0 section, with an internal conductor diameter Di, b) an external conductor that envelops the internal conductor in a radially equidistant manner, with an external conductor inner diameter Da, 5 c) an axially extending, common conductor section of internal and external conductor, along which, in equidistant intervals p, s rod-shaped structures with a rod diameter Ds that electrically connect the 0 internal conductor with the external conductor are provided , wherein, in order to allow the single TEM mode to propagate along the coaxial conductor structure unimpeded by higher excitation modes, which arise at least in the form of a TE 11 mode within m -5 frequency bands, the parameters Di, Da, Ds, p, s can be selected in such a way that i) A lower frequency limit fu(TEM) of the single TEM mode propagating within an n t 2-nd band is 30 equal to an upper offset-frequency fo(TEn 1 ) of the forming TE 11 mode in the m-th band ± of a tolerance range Af, and ii) An upper cut-off frequency fo(TEM) of the single 35 TEM mode propagating within an n 2 -nd band is equal to a lower cut-off frequency fu(TE 11 ) of the forming TE 11 mode in the (m+l)-th band of a tolerance range Af. 20

2. The coaxial conductor structure according to claim 1, wherein s is equal to 3 or 4. 5

3. The coaxial conductor structure according to claim 1 or claim 2, wherein the following applies for i): f,(TEM) = fo(TE11) ± lAfI with .0 f,(TEM)= (n-1)7r+ 2af(n-1)7r A 1+2a /(n - 1)2 / 72 as well as f%(TE11) = (m rf 0 + f, .5 as well as Af < (f, 7 ,., - fu,7-Mtu,n and .0 that the following applies for ii): f 0 (TEM) = f.(TEu) ± |MI with f%(TEM)= n n fo = nc 2p 25 as well as fu mr 2a/m/r 2 2 2 f.(TE 1 1 ) = ____ _+_I++2a / m' /;2'> 21 and with Zp Perturbation: a= ; 2cL 5 Impedance: Z 1 ln-"-; 2;r E Di Inductance: L =- "D -- D; s 2 4z D, Cut-off frequency: fo= , 2 zp .0 c 2 Cut-off frequency of the TEll mode: fc. - r D+D, wherein c:=light speed, p:=magnetic permeability, c:=dielectric conductance. .5

4. The coaxial conductor structure for the interference-free transmission of a single TEM mode of an HF signal wave within at least one band of n frequency bands forming within the framework of a dispersion relation, with n as a .0 positive natural number, with a) an internal conductor exhibiting a circular cross section, with an internal conductor diameter Di, 25 b) an external conductor that envelops the internal conductor in a radially equidistant manner, with an external conductor inner diameter Da, c) an axially extending, common conductor section of 30 internal and external conductor, along which, in equidistant intervals p, s rod-shaped structures with a rod diameter Ds that electrically connect the internal conductor with the external conductor are 22 provided , wherein, in order to allow the single TEM mode to propagate along the coaxial conductor structure unimpeded by higher excitation modes, which arise at least in the form of a TE 11 mode within m 5 frequency bands, with m as a positive, natural number, the parameters Di, Da, Ds, p, s can be selected in such a way that that an upper cut-off frequency fO(TEM) of the single TEM 0 mode propagating within the first, i.e., n=l, band is less than or equal to the lower cut-off frequency fu(TEu 1 ) of the forming TE 11 mode in the first band, i.e., m=l, wherein the following applies: c 6a 2 2 5 f%(TEM) = -- and und fu(TE 11 ) = 6af +f, . so that the following 2p 3+a applies: C 6a 2 - s5 f .fC" 2p 3+a .0 with c c 2 sZ p I fO=--C - and a=S'J" and Za=-- -Ini1 Da 2np r Da+D, 2cLr, 2;r E D

5. The coaxial conductor structure according to one of claims 25 1 to 4, wherein the rod-shaped structures situated in respectively equidistant intervals p of the internal and external conductor are arranged relative to the circumferential direction in such a way that the rod shaped structures are each congruently located one behind 30 the other in an axial projection to the axially extending, common conductor section, or the rod-shaped structures are offset in an axial sequence at an identical angular misalignment Act respectively oriented in the 23 circumferential direction of the internal and external conductor.

6. The coaxial conductor structure according to any one of 5 claims 1 to 5, wherein s is equal to at least 1.

7. The coaxial conductor structure according to claim 5 or claim 6, wherein 900 is equal to Ax. o

8. The coaxial conductor structure according to any one of claims 1 to 6, wherein the rod-shaped structures are made out of metal material.

9. The coaxial conductor structure according to any one of 5 claims 1 to 6, wherein the rod-shaped structures are made out of the same metal material the internal and/or external conductor are consisting of.

10. The coaxial conductor structure according to any one of 0 claims 1 to 6, wherein the tolerance range Af measures 1/3 of the bandwidth of the n-th TEM mode, i.e. lAfI< If,,..,n - fu,,M,n) 3

11. Use of a coaxial structure according to any one of claims 25 1 to 9 for interference-free signal transmission of a TEM mode of an HF signal wave within a frequency range in which higher excitation modes are not propagable, while simultaneously utilizing a local cooling of the internal conductor by providing thermally and electrically 30 conductive rod-shaped structures between the internal and external conductor.

12. The coaxial conductor structure according to any one of claims 1 to 9, wherein the internal conductor and/or 35 external conductor cross section of the coaxial line deviates from the circular shape, but exhibits the same impedance as the round coaxial line. 24

13. The coaxial conductor structure, substantially as hereinbefore described with reference to any of the figures. 5 25